Practical 1

 esreveR Engineering (heh)

For our very first practical activity, we were tasked with one major objective - to suggest ways to improve the energy efficiency of a drip-type coffee machine. There were two parts to this activity, namely to deconstruct the coffee machine to get a good idea of its inner workings, its different parts and their functions, and to understand how a drip coffee machine works. In the name of documentation, we took some photos every now and then to give you, dear blog readers, glimpses on the process of us doing the practical :)

Part 1: Reverse Engineering and Teardown

First off, we took apart the coffee machine (dubbed BD100) to see the internals that allowed it to brew that nice pot of brown gold (or brown water, if you like stronger coffee.) We used a screwdriver, some tweezers, and at some point, a little bit of force to open the stubborn lid to access its insides. Before that, we took apart the top half of the coffee machine which housed the water tank, permanent filter and filter holder.

After taking a good look at those parts, we turned BD100 on its head to open its bottom and look at the internals. We found that there was a tube that was in the shape of a horseshoe that wrapped around the heating element found at the bottom which connected to the power source.

We also found that this tube leads to two other tubes located at the back of the coffee machine, one leading from the water tank that had a small check valve, and the other leading to the top where the filter and the coffee grounds are put to be doused in hot water which will drip to the jug.

From this, we found out that in order to get water to the top of the machine, the coffee machine uses a bubble pump mechanism in which water that vapourises forms bubbles that in turn lower the overall density of water in the tube which allows it to rise, bringing along some hot water with it. This was a relatively inexpensive and simple way to get water to the top of the coffee machine, compared to other forms of artificial gas lifting such as using a compressor to do the same job. The heating element hence does double duty of not only heating the water but also getting water to the coffee grounds above.

The check valve we previously mentioned is key to this mechanism - by preventing the water from going backwards and back into the tank, it ensures that the water lifting only goes in one direction, which is up towards the filter.

After doing our observations, photo ops (of the pitiful, dismantled coffee machine) and raging over mismatched screws, we put the machine back together.

Part 2: Determining BD100's Energy Consumption

In the post-mortem of a poor coffee machine, we were tasked to then brew a cup of coffee (in a functional, non-dismantled machine, for safety reasons XD) to determine how much energy BD100 consumed, and from there, suggest ways to improve its energy consumption. We did so by first measuring a specific volume of water, weighing it and recording its temperature, then doing the same for the coffee and then getting to brewing. 

Using an electricity consumption monitor, we read the power rating for the machine as it was brewing a jug of coffee.

We then measured the temperature of the brewed coffee and the spent coffee grounds.

We also estimated the amount of water that vapourised and condensed on the lid of the water tank by comparing the mass of a dry paper towel to that of its mass when it was used to wipe the condensate off the lid. From all these data, we calculated the energy that was transferred to the coffee and hence was able to determine the energy efficiency of BD100 by calculating the energy transferred to the coffee divided by the electricity it consumed that was read off the electricity consumption monitor.

Conclusions

After some further research and discussion, we have come to the suggestion of designing the heating element as follows:

By having the water tube wrap around the heating element and have the wall of the water tube follow the curvature of the surface of the heating element. This ensures that there is more contact area between the water tube and the heating element and hence result in a better rate of heat transfer. For the hot plate, rather than just rely on the radiation of heat from the heating element to the hot plate, conduction of heat can instead take place by having the heating element have a flat part that is in contact with the hot plate.

And that concludes our activities for Practical 1: Reverse Engineering. :)